Television wave trap and the like



May 10,

Filed April 9,

E. SILVERMAN i 3% if 5% 0 /2 f/ao A 2 Sheets-Sheet l INVENTOR BY [MANUEL\SILVERMAN ATTORNEY y 10, 1955 E. SILVERMAN 2,708,238 TELEVISION WAVETRAP AND LIKE Filed April 9. 1954 2 Sheets-Shet 2 L; i 62/ I E ff CINVENTOR EMANUEL SILVER/WAN A TTORNEY United States Patent C) TELEVISIONWAVE TRAP AND THE LIKE Emanuel Silverman, Oak Park, Mich.

Application April 9, 1954, Serial No. 422,043

11 Claims. ((31. 250-20 This invention relates to means for eliminatinginterference in television receivers, for example, to eliminate FM,co-channel or adjacent channel interference. It is especially concernedwith an eflicient wave trap for eliminating the most extreme types ofadjacent channel interference.

In many television areas considerable difliculty is being presentlyencountered with adjacent channel interference which makes itsappearance as a slight herringbone effect on the television receiverscreen. In extreme cases as where the interfering channel is close byWhile the channel which it is desired to receive is at a distance,interference from the adjacent channel usually results in completobliteration of both picture and sound of the channel which it isdesired to receive. Similar obliteration results where the sound and/orpicture of a lower channel interferes with an adjacent higher channel.The latter has occured for example, where the lower channel has pictureand sound frequencies of 76 me. and 80 /2 me. respectively and thehigher channel has picture and sound frequencies of 82 Inc. and 86/2Inc. respectively.

Although various devices have been suggested and tried to eliminate theinterference in existing receivers none, insofar as I am aware, have,prior to my invention, successfully coped with the difficulty. Toattempt rebuilding the receiver to provide suitable circuiting to meetthe problem would, even if possible, be prohibitive. My invention makespossible a solution of the problem without need of disturbing theinternal mechanism of the receiver and with a minimum of effort on thepart of the service technician and low cost to the set owner.Accordingly, it is an object of my invention to provide means foreliminating FM, co-channel, and adjacent channel interference intelevision receivers.

Another object is to provide means for eliminating adjacent channelinterference of the type wherein the sound L and/or picture waves of alower channel interfere with and substantially obliterate the pictureand/or sound of an adjacent higher channel.

A further object is to provide a wave trap which will removeinterference of the foregoing character from any television receiverwithout the necessity of getting inside the receiver unit itself.

Still another object is to provide a variable wave trap adjustable tofacilitate the procurement of satisfactory reception from a givenchannel while providing means to attenuate interference from an adjacentchannel and such that the reception on both channels is withoutinterference.

A specific object is to provide a wave trap including a variable loopinductance adjustable to resonate over a band of frequencies andoperable for eliminating interference between adjacent channels withinsaid band.

A particular object is to provide a suitable housing for the adjustableloop inductance of the preceding object which housing will have a highdi-electric value i. e. low loss so as not to adversely affect thehigh-Q of the wave trap.

Another object is to provide means for eliminating or attenuatingextreme interference between adjacent channels of a television receiverby means of one or more wave traps having connctions in parallel withthe antenna tit) 2,703,238 Patented May 10, 1955 transmission line of atelevision receiver and preferably in juxtaposition to the receiveritself.

These and other objects of my invention will appear from the followingdescription and from the drawings illustrating preferred and relatedembodiments of m invention. 1

In the drawings illustrating my invention:

Figure l is a schematic view of one circuiting arrangement of myinvention utilizing as part of the wave trap a single loop inductancetype structure provided with a condenser control;

Figure 2 is a schematic view showing another circuiting arrangementutilizing a pair of wave traps of the character illustrated in Figure l;v

Figure 3 is a schematic view showing a further circuiting arrangement,similar to that in Figure 2 wherein one of the loop type wave traps isreplaced by an open circuit lead of predetermined wave length;

Figures 4 and 5 are schematic views of air di-electric and shorting bartypes of adjustable inductance loops which may be employed in thecircuiting of Figures 1 to 3 inclusive;

Figure 6 is a front elevational view partly in section of the singleloop type of inductance wave trap of Figure l;

Figure 7 is a side elevational view, partly in section of the wave trapof Figure 6; and

Figure 8 is a bottom view of the wave trap of Figure 6, a portion of thehousing for the loop inductance being broken away.

Broadly speaking my invention comprises an externally mountable wavetrap generally designated by the letter A which includes conductors 10,12 connecting it in parallel with the antenna transmission line of atelevision receiver and preferably at the antenna terminals of thetelevision set. My Wave trap preferably includes a pair of adjacent,that is to say, magnetic field coupled, high-Q tuned circuits generallyreferred to by the numerals 14 and 16 each connected at one side 13 onlyby the independent conductors 10, 12 to independent conductors 2%, 22respectively of the antenna transmission line generally designated bythe numeral 24 which line interconnects the antenna 25 and thetelevision receiver 28. The conductors 10, 12 together, may constitute atuned lead circuit of predetermined electrical wave length.

In general each high-Q circuit 14, 16 may comprise'an inductance,specifically a single loop inductance 26 and the connectors between theloops and the antenna transmission line illustrated as conductors 19, 12may comprise independent conductors of a section 30 of conventionalantenna transmission lead wire which may as described above constitute atuned circuit having a length, electrically speaking, which isapproximately M1 of a wave length of the interfering adjacent channel.However in many cases depending upon the character of the interferenceit will be found preferable to make this length less than /4 Wave length(i. e. a capacitance) and even quite short. In other cases the lengthmay be greater than A wave length (i. 'e. a lead inductance). Theinductance value of each loop in the circuiting should be such as tosubstantially result in a high-Q resonant circuit.

A further important feature of my invention is the mode of connectingthe parts of the wave trap and making connection thereof with thetelevision receiver installation. Thus I have discovered that in orderto obtain satisfactory results one side 18 of one loop inductance 14must be connected to the end of one conductor 10 of the tunedtransmission lead section 36 and one side 18 of the other loopinductance 16 must be connected to the same end of a second conductor 12of the section 30 and the opposite ends of these conductors 1t), 12 mustbe connected to the antenna transmission lead 24 by connecting oneconductor number to one conductor of the transmission lead 24 andconnecting the second conductor 12 to a .second conductor 22 of saidlead 24. By preference the latter connections will be made at theterminals 32, 34 provided on the receiving set 28 and to which theantenna transmission line or lead-in is connected.

. densers-36 may be in the form of variable mica trimmer capacitors, 38(see Figure 8). In actual practice I have found that capacitors of about10 to about 160 micromicrofarads .value are suitable for this purpose.Where such variable capacitors are employed the high-Q loops 26 will bepreferably physically out such that the inductive reactance of each loopis equal to the capacitive reactance of the capacitor 38 at the desiredresonant frequency.

Other forms of adjustment or control of the loop in ductauce such as avariable air dielectric or gap 40 as in Figure 4 or an adjustableshorting bar 42 on the loop for changing the length of the tuned line,as in Figure 5, may in particular cases be found serviceable in place ofa variable capacitor 38. I have further discovered that in certaininstances of extremeinterference a pair of .wave traps A and B (seeFigure 2) of the foregoing character may be desirably utilized to removethe sound and/ or picture waves of the interfering channel. In suchinstances one of the wave traps A will preferably be connected asdescribed above to the antenna terminals 32, 34 on the set 23 and theother trap B will be connected to the antenna transmission line 24 at apoint spaced electrically speaking from such terminals of thetransmission line approximately of an electrical wave length.

It'will also be found possible in certain cases of interference toinhibit the same by utilizing one wave trap A as described above at theantenna terminals 32, 34 and connecting an open lead 52 of approximatelyone-quarter wave length in parallel with the antenna transmission line24 at the point 50 a distance of approximately threeeighths of anelectrical wave length from the connection of the first wave trap Athereto.

In most instances of installation it will be found desirable, for thesake of good appearance, to provide some form of housing 56 for the loopinductances of the wave form of the high-Q magnetic field coupled, tunedcircuits 14, 16 and connectors 10, 12of my invention. Such convenientlycomprises a housing 56 having a dished casing I 60 of substantiallyelongated rectangular form preferably made of a low loss synthetic resinplastic of the aforesaid types and having a back wall 62, side walls 64,66, and end walls 68, 70. To this casing is secured as by cementing acover 72 of similar material to the casing.

Arranged interiorly of the housing 56 and spaced from the walls thereofare the pair of symmetrically arranged single loop inductances 26 whichare arranged in spaced apart faceto face relationship so as to beseparated by an air gap 76 and be magnetically coupled. 7 As seen eachloop comprises a generally U-shaped metallic rod for example aluminum,shown here as inverted and across the legs 78, 80 of which are securedas by screws 82, 84 the upstanding opposite terminals 86, 88 ofconventional plate-type trimmer capacitorsor variable condensers 38 elf)preferably of 10 to 160 micromicrofarads capacity, each provided with anadjusting screw 92 for varying the capacity of the condenser between thelimits thereof. The condensers 38 are mounted by their insulated bodies94 to a metallic cross bar or plate 96 by suitable means such asmetallic ears 98 associated with the condenser. The plate 96 is securedas by a screw 100to a boss 102 of insulation material projectinginwardly from the wall 70 of the housing 56 centrally thereof and whichmay be an integral part of the casing. It will be observed that theloops 26 are securely supported in a parallel upright manner, with theirleg'portions parallel to each other and equally spaced from each other,by the condensers 38 whichin turn are supported by the plate 96 tothehousing.

Therear wall 62 of the housing 56 is provided with an aperture 106through which is projected the aforesaid section 30 of a two conductorantenna transmission lead wire described above. Oneof the conductors .10

of this lead connects with one of the loops 26 by a terminal connector108 held under the screw 84, and the second conductor 12 is similarlyconnected with the 'other of the pair of loops 26 by a terminalconnector 110. The opposite ends of the conductors 10 and 1.2 areprovided with terminal connectors 112, 114.

In using the unit of Figures 6 to 8 the two terminals 112, 114 of theconductors 10 and 12 respectively of the wave trap are attached forexample and by preference to the antenna terminals 32, 34 on thetelevision receiver. The television receiver is then allowed to warm upfor at least five minutes. 58 of the wave trap in hand the screws 92 ofthe trimmer capacitors 38 are alternately adjusted about one-eighth turnat a time, through the openings of the housing 56 and carefulobservation is made of any interference while turning either one of thescrews 92.

After adjusting for minimum interference the housing 56 is mounted inany suitable manner to the rear of the television receiver, as far aspossible from the chassis.

The lead 30'should not be coiled but allowedto hang free. After mountingthe housing to the set a final adjustment of the wave trap for minimuminterference is usually desirable.

Wherever the term wave length is used in the specification and claims,it is intended to mean the wave length of the undesired wave and itsvalue may be determined from the electrical wave length of the frequencyof the station to be attenuated. Moreover, the term Q as used herein isa factor representing the sharpness at resoname of the tuned circuit.The Q is high when the sharpness at resonance of the circuit when tunedto the sound carrier of the lower adjacent channel is such that the bandwidth of the resonant curve is sufliciently narrow so that it does notappreciably attenuate the upper channel video carrier. Since the upperchannel video'carrier is separated from the lower adjacent channel soundcarrier by about 1 /2 megacycles the 'band width of the curve of thetrap at resonance for a high Q condition should preferably not begreater than about one megacycle at the half power point. 7

From the foregoing description of my invention it will be apparent thatI have provided a novel and efiicient wave trap for substantiallyeliminating interference in television receivers especially interferencebetwen adjacent channels and which wave trap is well adapted for suchpurposes. It will be understood that various changes and modificationswill suggest themselves to those skilled in the art in the specificstructure disclosed Without departing from the spirit and intent of myinvention. Accordingly all such changes, modifications and equivalentstructures coming within the scope of the appended claims arecontemplated.

I claim: I Y I 1. In a television receiving system having a receivingunit, an antenna and a two wire transmission line be.-

Thereafter and with the housing tween the receiving unit and theantenna, means for attenuating interference in reception at thereceiving unit comprising a pair of electrically coupled and tunableloop inductances, each of said inductances having two impedance coupledterminals, and each of said inductance". being connected to a separatewire of said transmission line at a single point thereon through one ofits associated terminals.

2. In a television receiving system having a receiving unit, an antennaand a two wire transmission line between the receiving unit and theantenna, means for attenuating interference in reception at thereceiving unit comprising a pair of inductively coupled and tunedinductances, each of said inductances having two terminals and the saidtwo terminals of each inductance being coupled by an impedance, each ofsaid inductances being directly connected to separate wires of saidtransmission line through only one of its said two terminals and theother terminal of said two terminals of each inductance being connectedto the same transmission Wire through its ass:- ciated impedance couple.

3. In a television receiving system having a receiving unit, an antennaand a two wire transmission line between the receiving unit and antenna,means for attenuating interference in reception at the receiving unitCOW- prising a pair of electrically coupled loop inductances and a pairof capacitors couplirn the terminal ends of said pair of loopinductances to form a pair of tuned circuits, one capacitor coupling theterminal ends of one loop inductance and the second capacitor couplingthe terminal ends of the other loop inductance, one of said two wires ofsaid transmission line being connected to a single one of the terminalends of said one loop inductance, and the second wire of saidtransmission line being connected to a single one of the terminal endsof the said other loop inductance, and the other terminal ends of saidone and said other loop inductances connecting with said transmissionline only by way of said tuned circuits.

4. In a television receiving system having a receiving unit, an antennaand a two wire transmission line between the receiving unit and theantenna, means for attenuating interference in reception at thereceiving unit comprising a pair of electrically coupled and tunableloop inductances providing a pair of tuned circuits, each of saidinductances having two impedance coupled terminals and a tuned lineconnecting said inductances with said transmission line, said tuned linecomprising two conductors one connecting a single terminal of one ofsaid inductances with one wire of said transmission line and the secondconductor connecting a single terminal of ti": other of said inductanceswith the second wire of said transmission line, the other terminals ofsaid inductances connecting with said transmission line only throughsaid tuned circuits.

5. In a television receiving system having a receiving unit, an antenna,and a two wire transmission line between the receiving unit and antenna,means for attenuating interference in reception at the receiving unitcomprising a pair of inductively coupled inductances each having twoterminal ends, separate capacitor means co"- pling the two said terminalends of said inductances and adapted to etfect resonant tuning of saidinductances, and electrical means connecting each of said inductances toa separate wire of said transmission line at a single point thereonthrough one of its associated terminal end 2.

6. In a television receiving system having a receiving unit, an antennaand a two wire transmission line between the receiving unit and theantenna, means for attenuating interference in reception at thereceiving unit comprising a pair of electrically coupled and tunedinductances each providing a tuned circuit, each inductance comprising aU loop inductance having a capacitance coupling its opposite legs, meansconnecting one wire of said transmission line with a single leg of oneof said U loops, and means connecting the second wire of saidtransmission line with a single leg of the other of said U loops, theother legs of said U loops connecting with said transmission line onlythrough said tuned circuits.

7. An interference attenuating means as claimed in claim 6 wherein thecapacitance coupling the legs of the U loop inductances are variablecondensers and wherein the corresponding legs of said loops are inface-to-face relationship.

8. An interference Wave trap for a television receiving means having areceiving unit, an antenna, and a two wire transmission line between thereceiving unit and antenna said trap comprising a pair of loopinductances arranged in juxtaposed and electrically coupledrelationship, a first electrical terminal means connecting with a singleleg of one of said loop inductances, a second electrical terminal meansconnecting with a single leg of the other of said loop inductances, andmeans for effecting tuning of said trap comprising a first capacitancecoupling the legs of one of said pair of loop inductances, and a secondcapacitance coupling the legs of the other of said pair of loopinductances, each of said inductances being adapted to be connected to aseparate wire of said transmission line at a single point thereonthrough its associated electrical terminal means.

9. In a television receiving system having a receiving unit, an antennaand a two wire transmission line between the receiving unit and theantenna, means for attenuating interference in reception at thereceiving unit comprising a pair of electrically coupled and tunableinductances each inductance comprising a substantially U loop inductancehaving shorting bar means coupling its legs and forming therewith atuned circuit and means connecting each wire of said transmission linewith a single leg of a different one of said two loop inductances, theother legs of said loop inductances connecting with said transmissionline only through said tuned circuits.

10. The combination as set forth in claim 1 including a second pair oftunable loop inductances similarly connected to said transmission lineat a position thereon a predetermined Wave length from the firstmentioned pair of said loop inductances.

11. A wave trap for attenuating interference in television receiverscomprising a housing of high dielectric material having surroundingwalls, a plate mounted in one end of said housing adjacent a wall atthat end, a pair of variable capacitors mounted in spaced relation onsaid plate and having their opposite terminals transversely of saidplate, a pair of substantially U-shaped loop inductances of bar materialcarried by said plate and in spaced relation to the walls of saidhousing, one of said inductances having its legs connected to the saidopposite ter minals respectively of one of said capacitors and the otherinductance being similarly connected to the other capacitor, said loopinductances as so connected having their corresponding legs face-to-faceto each other and at such spacing as to establish an inductively coupledrelationship therebetween, a conductor connecting with a single terminalof one of said capacitors and a second conductor connecting with asingle terminal of the other of said capacitors, each of said loopinductances being adapted to be connected to a separate wire of a twowire transmission line at a single point thereon through its saidassociated conductor.

References Cited in the file of this patent OTHER REFERENCESElectronics, October 1945, pages and 152.

